Old instrument players occasionally taking ecstasy (4)
I believe the answer is:
lyre
'old instrument' is the definition.
(I've seen this in another clue)
'players occasionally taking ecstasy' is the wordplay.
'occasionally' indicates alternate letters.
'taking' is a charade indicator (letters next to each other).
'ecstasy' becomes 'E' (informal term for the drug).
The alternating letters of 'players' are 'lyr'.
'lyr'+'e'='LYRE'
(Other definitions for lyre that I've seen before include "Old instrument, like a harp" , "Old stringed instrument" , "Old musical instrument with strings in U-shaped frame" , "Ancient Greek stringed instrument" , "Ancient stringed musical instrument with U-shaped frame" .)